lib/crypto: curve25519-hacl64: Fix older clang KASAN workaround for GCC

commit 2b81082ad37cc3f28355fb73a6a69b91ff7dbf20 upstream.

Commit 2f13dae ("lib/crypto/curve25519-hacl64: Disable KASAN with
clang-17 and older") inadvertently disabled KASAN in curve25519-hacl64.o
for GCC unconditionally because clang-min-version will always evaluate
to nothing for GCC. Add a check for CONFIG_CC_IS_CLANG to avoid applying
the workaround for GCC, which is only needed for clang-17 and older.

Cc: [email protected]
Fixes: 2f13dae ("lib/crypto/curve25519-hacl64: Disable KASAN with clang-17 and older")
Signed-off-by: Nathan Chancellor <[email protected]>
Acked-by: Ard Biesheuvel <[email protected]>
Link: https://lore.kernel.org/r/20251103-curve25519-hacl64-fix-kasan-workaround-v2-1-ab581cbd8035@kernel.org
Signed-off-by: Eric Biggers <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: nathanchance

lib/crypto/Makefile

@@ -48,7 +48,7 @@ libcurve25519-generic-y				:= curve25519-fiat32.o
 libcurve25519-generic-$(CONFIG_ARCH_SUPPORTS_INT128)	:= curve25519-hacl64.o
 libcurve25519-generic-y				+= curve25519-generic.o
 # clang versions prior to 18 may blow out the stack with KASAN
-ifeq ($(call clang-min-version, 180000),)
+ifeq ($(CONFIG_CC_IS_CLANG)_$(call clang-min-version, 180000),y_)
 KASAN_SANITIZE_curve25519-hacl64.o := n
 endif